Depolarization ratios of resonance Raman scattering in the gas phase

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Abstract
All three scattering invariants, isotropic, antisymmetric, and anisotropic, contribute to the resonance Raman (RR) activity of randomly oriented gas phase scatterers as shown in a sum‐over‐all‐rovibronic‐states approach regardless of the symmetry of the vibrational transition. Thus, in the gas phase, totally symmetric modes may have Raman depolarization ratios (ρ)>3/4 and nontotally symmetric modes may have ρ≠3/4 for resonance excitation frequencies. Large ρ dispersion effects are predicted when the RR scattering cross section is dominated by the contribution of a single vibronic band. The extent of this purely rotational effect sensitively depends on the excitation frequency and the resonant dephasing rate. These depolarization ratio effects are demonstrated by the resonance Raman scattering of CH3I (B state) and NH3, ND3 (A state) for both a and e vibrational bands as well as for J (NH3) and K (CH3I) resolved rovibrational features.